The coefficient of thermal expansion (CTE) of a polymer material—specifically, a cured epoxy resin compound is about 50 to 80 ppm/° C., which is very high, several to tens of times larger than the CTE of a inorganic material, such as ceramic material or a metal (for example, the CTE of silicon is 3 to 5 ppm/° C., and the CTE of copper is 17 ppm/° C.). Thus, when the polymer material is used along with the inorganic material or the metal in a semiconductor, a display, or the like, the performance and processing of the polymer materials would be remarkably limited due to the different CTEs of the polymer material and the inorganic material or the metal. In addition, during semiconductor packaging in which a silicon wafer and a polymer substrate are used side by side, or during a coating process in which an inorganic shielding layer is coated on a polymer film to impart gas barrier properties, product defects such as the crack formations in an inorganic layer, the warpage of a substrate, the peeling-off of a coating layer, the failure of a substrate, and the like, may be generated due to a large CTE-mismatch between constituent materials during processing and/or service temperatures.
Because of the large CTE of the polymer material and the resultant dimensional change of the polymer material, the development of next-generation technologies in the fields of semiconductor substrates, printed circuit boards (PCBs), packaging, organic thin film transistors (OTFTs), and flexible display substrates, and the like may be limited. Particularly, the semiconductor and PCB industries have been challenged in the design of next generation parts requiring a higher integration and miniaturization, flexibility, superior performance, and the like, and securing processability and reliability of the parts due to the polymer material having a very higher CTE compared with metal/ceramic materials. In other words, due to the high thermal expansion properties of the polymer material at processing temperatures, defects may be generated, processing may be limited, and the design, processability and reliability of the parts may become objects of concern. Accordingly, improved thermal expansion properties or the dimensional stability of the polymer material are necessary in order to secure processability and reliability of electronic parts.
In general, in order to improve the thermal expansion properties—i.e., to obtain a low CTE of a polymer material such as an epoxy compound, (1) a method of making a composite of the epoxy compound with inorganic particles (inorganic filler) and/or a fiber or (2) a method of designing a novel epoxy compound having a decreased CTE have been used.
When the epoxy filler composite, which is a composite of epoxy compound and inorganic particles is formed in order to improve thermal expansion property, a large amount of silica particles of about 2 to 30 μm is required to decrease the CTE sufficiently. However, due to the addition of the large amount of inorganic particles, the processability and the physical properties of the parts may be deteriorated. That is, the large amount of inorganic particles may decrease fluidity, and voids may be generated due to the insufficient filling of narrow spaces. In addition, the viscosity of the material may increase exponentially due to the addition of the inorganic particles. Further, the size of the inorganic particles tends to decrease due to semiconductor structure miniaturization. When a filler of 1 μm or less is used, the decrease in fluidity (viscosity decrease) may become even more serious. When inorganic particles having a larger size (average particle diameter) are used, the insufficient filling of the filler composite occurs more frequently. While the CTE of an organic resin may be largely decreased by making glass fiber composite, the CTE however, may still be high when compared to a silicon chip or the like.
As described above, the manufacturing of highly integrated and high performance electronic parts for next generation semiconductor substrates, PCBs, and the like may be limited due to the limitations of composite technology for epoxy compounds. Thus, the development of polymer composite having improved heat resistant properties,—namely, a low CTE and a high glass transition temperature—is required to overcome the challenge of a lack of heat resistant properties due to a high CTE and processability of a common thermosetting polymer composite.